Saturday, 29 January 2011

There are two current taxonomy trends: (1) the recognition of new species by splitting traditional species and (2) the dwindling number of valid subspecies. The concept of subspecies is much fuzzier than that of species, and a vast number of ostensible subspecies has been built up on the basis of tiny size or plumage variations. In species of a wide range the usual process is a progressive clinical variation on a continental scale. There are many examples. In the case of the larger mammals, all well studied, the scores of described subspecies of wolves or leopards have been whittled down to a handful (even the "Iberian" wolf has lost its status though the term "signatus" is still sometimes used by inertia). The same goes for birds. Witness a recent study (Campos et al., 2010) on the White-Throated Dipper (Cinclus cinclus), with two recognised subspecies in Spain according to the usual textbooks and guides: cinclus in the northeast and centre and aquaticus in the east and southeast. The supposed distinguishing feature is the colour of the underparts below the white bib: blackish in cinclus and chestnut in aquaticus. But the authors of this work, after capturing 301 Dippers in 37 rivers from 10 different areas in Spain from 2000 to 2007, have shown that there are in fact individuals of both types in nearly all regions; three of the ten birds recaptured even showed both colour patterns on different dates. Neither were any biometric differences recorded. The conclusion is that the underparts colour is not a sufficient condition for differentiating Dipper subspecies in Spain. Nonetheless, although the range of both forms shows no clear pattern, the cinclus type was more frequent in the centre and north of Spain and was not observed in the southeast. In Extremadura only one river was sampled, for which no details have been given. In the set of six rivers sampled in Gredos a total of 55 birds were observed, 86% of them cinclus. To illustrate all the above we print below two photographs taken on the River Jerte by the colleagues of Objetivo Verde (our thanks go to José Luis Rivero).

Monday, 24 January 2011

A couple of weeks ago we duly reported the first ever Extremadura Goosander record (Mergus merganser) (click here), with further general information on this rare vagrant and the unprecedented Spanish "irruption" this year compared to the dearth over the last 25 years. The star of that entry, a first-winter female, stuck around in the same Plasencia lake until at least Sunday 23 January (Javier Gayo and Sergio Mayordomo). But it wasn't the only one to get here; on 21 January J. M. Benítez observed a first winter female in Torrejón-Tiétar Reservoir, right in the middle of Monfragüe nature reserve (communicated by Ángel Sánchez). There was some doubt about whether or not it was the same bird, since there is a distance of only 26 km or so between both sites. Thanks to the detective work of S. Mayordomo, however, we now know they are different birds, since he saw both in one morning on the 23rd (the Monfragüe bird was also seen by Manuel García de Rey and Martin Kelsey, among others).

Sunday, 16 January 2011

Bonelli's Eagle (Aquila fasciata). One of the two adults currently tracked by satellite in the province of Badajoz (Ángel Sánchez).

Satellite tracking is giving us enormous insights to the movements of birds. One single tagged bird produces more information than hundreds or thousands of birds marked with the traditional metal rings (or bands in US). It is also much more informative than distance reading of colour rings, above all in species hard to get close to, like raptors. Although the results are more eyecatching in migratory birds (see Egyptian Vulture), they can also be revealing in the case of sedentary birds like the Bonelli's Eagle (Aquila fasciata). At the moment there are two satellite tracked adults in the Extremadura area called "La Siberia". Given that their movements are restricted to their nesting zone (Ángel Sánchez, pers. obs.), the detailed information has obviously not been made public. Applied to juvenile birds in dispersal, however, the system is less hermetic. We have found two studies of this dispersal, one from Portugal, which could be perfectly extrapolated to the Extremadura population,and the other from the Spanish Mediterranean arch.

In the first case four Bonelli's Eagles chicks were tagged in the nest and then tracked for three to seven months afterwards. The two born in the Duero moved on to the Rías Baixas en Galicia. One was shot dead and the signal was lost from the other, maybe due to a technical fault. The two eaglets born in the Tagus area (one on the border with the province of Cáceres) also moved north as juveniles, to Galicia and Asturias. After a few months the signals were lost; in one case death is suspected due to unknown causes; the other case is put down to a technical hitch.

Movements of four satellite-tracked young Bonelli's Eagles (Aquila fasciata) from Portugal [in yellow, the movements of a Golden Eagle (Aquila chrysaetos)].

The Mediterranean area study was conducted on 14 young birds from 9 nests between Barcelona and Murcia. During their first year these birds stuck pretty close to the nest; then they dispersed over much of the Iberian Peninsula before settling down for varying periods in one or other dispersal area. A total of 16 areas were identified in prey-rich farming areas with no breeding adults. None of these dispersal areas was in Extremadura, though two birds did make brief stopovers in the province of Cáceres (Sierra de Gata and Llanos de Trujillo)..Juvenile dispersal areas of 14 birds (top) and first-year movements of seven Bonelli's Eagle (Aquila fasciata) juveniles born in the Spanish Mediterranean Arch (bottom).

Monday, 10 January 2011

Goosander (Mergus merganser), first winter female. La Torrecilla, Plasencia, Cáceres. 09-01-11. Top, resting on land among a small flock of Teal (Anas crecca); Bottom, swimming next to a female Shoveler (Anas clypeata). Photographer: Javier Prieta. See more photographs.

Extremadura clocks up another first, the third new species since this blog came online eight months ago in May 2010. The species this time is Goosander (Mergus merganser), joining the Pied Billed Grebe and Buff-Breasted Sandpiper, which featured in earlier blog entries.

The sawbills are fish-eating diving ducks that take their name from the serrated edges of their thin beaks. A solitary female Red Breasted Merganser (Mergus serrator), spotted by Santiago Villa in Brozas back in March 1997, was hitherto the only sawbill previously seen in Extremadura. Now another young female, this time of its cousin species the Goosander, found by Sergio Mayordomo in Plasencia on 9 January 2011, can be added to this meagre list (other observers: Ricardo Montero and Javier Prieta; on 11 Jan was found by SM, JP, Miguel Ángel Muñoz y Eva Palacios).

The Goosander breeds in the Taiga of North America and Eurasia, wintering further south but without reaching Spain, where it is classed as a rare vagrant. From 1984 to 2008 there were only 28 accepted records involving 62 birds, all on mainland Spain (CR-SEO, 2006-2010). In Portugal it has been recorded only twice (Catry et al. 2010). According to De Juana (2006) it turns up in Spain only when driven further south by cold spells on continental Europe, so some years there are no records at all. Until 2003 only one bird among 28 records turned up in an inland province (Navarre) and only two were in the southern half of the country (Albufera de Valencia and Odiel, Huelva). All the birds were recorded between November and March, with 83% of the birds being seen in only three winters, females clearly outnumbering drakes (2:1). In the 2004-2008 period only five single birds were accepted (CR-SEO, 2006-2010); these records were atypical since three of the birds turned up inland (Huesca, Ciudad Real-Toledo and Granada) and two of them were in spring (one in May and the other in June). In 2009, a year for which the rarity report has not yet been published, there were several typical records in Galicia and Asturias and another in Zamora (Rare Birds in Spain).

The cold snap that hit the centre and north of Europe in December 2010 produced a considerable influx of Goosanders into Spain. To find something similar we need to go right back to 1984-1985, with 6 records involving a total of 22 birds. The first bird appeared on 04/12/2010 with over 30 birds then being observed in 20 different sites in 15 provinces by 10/01/2011. As well as the sheer number, this wave of observations is also notable for the total lack of drakes, only females being seen, and also because over half of the provinces involved, 8, were inland (sources: Rare Birds in Spain and Reservoir Birds).

A previous entryof this blog gave a brief account of Spoonbill breeding in Extremadura from 2000, when breeding was first confirmed, to 2009. A best-guess figure was also given for 2010. Now that all the 2010 figures are to hand, we offer the actual info as a worldwide scoop!

The four habitual breeding colonies were visited in 2010. One of them lacked any Spoonbills and the other had succumbed to the rising waters of a reservoir. Happily the birds themselves shifted to a new site, although it was not found until June, when a single count was made. The other two colonies were visited several times. An occupied nest with no clutch was also found in a new locality.

The total 2010 Spoonbill breeding population in Extremadura was 50 pairs, shared out among four colonies: Monfragüe and environs (23), Montijo Reservoir (16), Alqueva Reservoir (10) and Alagón Valley(1). This is the biggest known figure, so the birds are still on an upward trend. Participants: Javier Prieta, Sergio Mayordomo, Emilio Costillo and Agustín Mogena.